It is known that the efficiency of an automotive air conditioning system depends on the refrigerant gas used, which in addition to obviously corresponding to a specific type of refrigerant gas specified by the vehicle manufacturer, must have a certain level of “purity” with regard to other types of gas, henceforth indicated as “contaminant gases”.
In the real world, it often happens that the refrigerant gas in the system becomes impure, i.e., it becomes accidentally mixed with a quantity, albeit minimal, of contaminant gases. Refrigerant gas contamination can be intrinsically present from source, i.e., present in the refrigerant gas used when first charging the air conditioning system, or it can happen after the initial charging, for example, due to service operations on the automotive air conditioning system or the substitution of one type of refrigerant gas with another type of refrigerant gas.
Nowadays, the above-mentioned risk of contamination is a very real problem in the automotive industry, as regulations have been introduced that require the refrigerant gas R-134 currently used in automotive air conditioning systems to be replaced with a new type of refrigerant gas R-1234yf, different from the old one.
To this end, the need has arisen in the automotive industry to make gas analyzer systems configured to determine, with a certain accuracy, the type and actual concentration of the refrigerant gas actually in the automotive air conditioning system, in order to establish whether the latter meets the above-indicated regulations.
Some of the currently known refrigerant gas analyzer systems function using NDIR (Non Dispersive InfraRed) technology and normally include: an inlet terminal that can be connected to a connector on the low pressure system to receive the refrigerant fluid in the gaseous state at a constant predetermined pressure; a gas analysis chamber; a pressure reduction device, arranged between the inlet terminal and the gas analysis chamber to supply the refrigerant gas to the latter at a reduced pressure with respect to the pressure of the gas leaving the low pressure circuit, typically a pressure higher than the ambient pressure; an infrared radiation emission source configured to emit a radiation beam in the infrared frequency band inside the gas analysis chamber; an infrared multi-detector device configured to generate an electrical signal having an electrical quantity that is indicative of the radiation absorbed by the gas in certain frequency bands; and an electronic control circuit to determine the concentration of the refrigerant gas inside the analysis chamber, based on the electrical quantity generated by the multi-detector device.
The above-described gas analyzer systems are typically configured to perform an initial automatic calibration, during which the electronic control circuit determines a reference electrical quantity, normally a voltage, which is indicative of a condition of absence of gas in the analysis chamber and which is associated with an absolute reference value, in particular, a null gas concentration, henceforth indicated as the zero reference. The reference electrical quantity associated with the zero reference is then used in calculating the refrigerant gas concentration. In the case in point, the automatic calibration is performed by feeding air taken from the outside environment through an active-carbon filter and into the analysis chamber, generating the radiation beam in the chamber and assigning the electrical quantity generated by the multi-detector device in the presence of ambient air in the analysis chamber to the reference electrical quantity.
Unfortunately, the calculation of the reference electrical quantity performed by means of the above-described initial automatic calibration suffers from an intrinsic error based on the presence of contaminant gases in the outside ambient air used for reference. Laboratory tests performed by the applicant have in fact demonstrated that air taken from the outside environment, even if filtered using an active-carbon filter, is not pure, but contains significant percentages of contaminant gases such as, for example, CO2, CO etc. Thus, the presence of contaminant gases contained in the ambient air during calibration introduces an intrinsic error into the reference electrical quantity and, in consequence, in the calculated concentration of the refrigerant gas, thus causing a reduction in the accuracy of the analysis.
It is also known that for the purposes of increasing the precision in measuring the concentration of the refrigerant gas, the need has lately arisen to be able to determine with high precision, not just the percentage of the high-concentration gas, namely the refrigerant gas, but also the percentage of “low concentration” gases, or rather the contaminant gases, so as to have comprehensive information on the composition of the gas present in the automotive air conditioning system.
However, this need has not yet been satisfied due to certain technical problems that have remained unsolved up to now and basically derive from the difficulty of sizing the analysis chamber in an adequate manner, both for the analysis of the refrigerant gases present with high concentrations and for the analysis of contaminant gases present in low concentrations.
In particular, laboratory tests performed by the applicant on analyzer systems of the above-described type, in which it is contemplated maintaining the gas in the analysis chamber at a pressure substantially equal to the ambient pressure, have demonstrated that increasing the containment volume of the gas inside the analysis chamber causes, on one hand, a corresponding increase in the precision of measuring gases present in low concentrations, but, on the other hand, a progressive reduction in the precision of measuring the gas with a high concentration, a typical condition faced in the case of analysing refrigerant gases, up to the point of arriving to a state where analysis is impossible. In fact, the presence of a high refrigerant gas concentration in a particularly “large” chamber volume causes high absorption of energy from the radiated beam, which if expanded beyond a certain volume threshold induces a saturation condition in the electrical signal generated by the multi-detector device that renders analysis of the gas impossible.
Conversely, by keeping the pressure of the gas in the analysis chamber substantially equal to the ambient pressure and reducing the internal volume of the analysis chamber, greater precision is obtained in measuring the high-concentration gas, as the number of moles of gas analysed is reduced, in this way avoiding the risk of saturation for the multi-detector device, but at the same time, the precision in measuring the low-concentration gases is reduced because the number of moles able to absorb the radiation is extremely low and becomes undetectable by the multi-detector device.
Lastly, the above described analyzer systems are configured to discharge the analysed gas contained in the analysis chamber into the outside environment, with all of the consequences that this entails from the standpoint of environmental pollution.